Greenpeace activists have been arrested after they occupied a French nuclear power plant site.

Around 30 activists from the environmental group invaded state-owned nuclear power utility Electricite de France's Tricastin power plant complex in southern France.

By midday, all but two of the activists had been arrested and were being held in a nearby police station, Greenpeace France said on its web site.

The media stunt is deeply embarrassing to the government which is intent on demonstrating that France's reliance on nuclear power is safe.

The activists projected a video on the side of one of the plant's buildings which said "Tricastin Nuclear Accident" and showed the image of a giant crack forming across the building's facade.

Activists also hung a giant banner with president Francois Hollande's face and the words "President of the Catastrophe?"

France's nuclear safety authority said in a statement that so far the intrusion had had no impact on the plant's safety.

France is among the most nuclear-dependent countries in the world, with reactors producing about 80% of its electricity.

In 2008, the Tricastin plant reported several incidents that angered anti-nuclear groups, including a leak of unenriched uranium into two nearby rivers and the release of radioactive particles from a pipe.